The present invention relates to a liquid crystal display panel for a timepiece for displaying at least either of time information such as an hour, a minute, and a second, or calendar information such as a date, days of the week, a month, and a year by use of a liquid crystal display panel, and more particularly, to not only a liquid crystal display panel for indicating digital display of time information and calendar information but also a liquid crystal display panel for a combination timepiece for indicating digital display and analog display of time information by hands, or an analog timepiece for indicating markers and so forth on a dial thereof, or for indicating simulated hands for an hour hand, a minute hand, and a second hand, by the liquid crystal display panel. The timepiece includes a watch and a clock.
A timepiece for indicating digital display of time information such as an hour, a minute, and a second, and calendar information such as a date, days of a week, a month, a year, by use of a liquid crystal display panel, has been in widespread use for wrist watches and clocks, provided with a crystal oscillation circuit.
There has also been in use a combination timepiece in which analog display for indicating time information by the hands of the watch is used in combination with digital display indicating time information and calendar information in numbers and letters.
Further, there has also been proposed an analog timepiece for selectively displaying markers in various patterns, or for displaying simulated hands for an hour hand, a minute hand, and a second hand, by providing the dial thereof based on a liquid crystal display panel (referred to, for example, Japanese Patent Laid-open S54-153066).
In a conventional liquid crystal display panel for displaying time information and calendar information, used in such a timepiece, a liquid crystal cell which is filled with a liquid crystal is sandwiched between two transparent substrates having an electrode on respective inner surfaces thereof, facing each other, and an upper polarizing film and a lower polarizing film are disposed, respectively, on the external surface of the substrates. If an electric field is applied to the liquid crystal by applying a voltage between a pair of electrodes on the substrates of the liquid crystal cell, the optical characteristic of the liquid crystal is changed, thereby locally controlling transmission and absorption of light made incident on the liquid crystal display panel such that a predetermined display is effected.
As the liquid crystal, a twisted nematic (TN) liquid crystal having a twist angle of less than 90xc2x0 is mainly used, and a super twisted nematic (STN) liquid crystal having a twist angle of 170xc2x0 to 240xc2x0 is occasionally used.
Either of the upper polarizing film or the lower polarizing film is a polarizing film absorbing the light linearly polarized in the direction orthogonal to the transmission axis thereof.
In the case of a timepiece using the conventional liquid crystal display panel described above, time information and calendar information are displayed in black against a white background in a normally white mode that is common.
However, by simply displaying time information and calendar information in black against the white background as described in the foregoing, neither variation in design nor interest can be offered, with a resulting tendency to lose soon popularity with consumers. Probably, as a result, consumption of digital timepieces has recently been on the decline, and neither combination timepieces nor analog timepieces with a liquid crystal display panel have since received market acceptance.
In light of the present situation as described, the invention has been developed, and an object thereof is to provide a liquid crystal display panel for a timepiece capable of providing attractive variation in design while indicating a digital display or an analog display.
In recent years, a liquid crystal display panel having a liquid crystal layer containing a liquid crystal and a polymer material has been developed. It is expected to improve visibility of a digital timepiece as well as decoration of the liquid crystal display panel thereof, by displaying time information, calendar information, and the like through the use of the liquid crystal display panel for the timepiece.
The liquid crystal display panel having a liquid crystal layer containing a liquid crystal and a polymer material employs a light scattering type liquid crystal cell, therefore it can transmit almost all incident light because it does not need a polarizing film and an alignment film. Accordingly, the liquid crystal display panel effects high utilization efficiency of light, thereby displaying a bright white screen by virtue of its becoming opaque white.
This type of liquid crystal cell is broadly divided into a polymer network type and a polymeric dispersed type. In a polymer network liquid crystal cell, a polymer is formed into compact and random three-dimensional network structure in continuous layers of a liquid crystal, and the liquid crystal is aligned at a wall of the polymer network. Therefore, the liquid crystal layer becomes a uniform optical anisotropic medium to scatter light strongly.
The polymer dispersed liquid crystal cell, in which a liquid crystal forms minute particulate drops and is dispersed in a polymer medium, scatters light at the interface of the liquid crystal and the polymer due to inconsistency of their refractive indexes.
At this moment, a projection-type liquid crystal display device and a reflection-type liquid crystal display device with the liquid crystal display panel using a mixed material of a polymer material and a liquid crystal for the liquid crystal layer have been developed. However, in regard with an application of the liquid crystal display panel for a timepiece, there is only a case where a liquid crystal display panel is placed on the glass side of the timepiece and its user presses a button of a setting-terminal input portion to apply a voltage to the scattering type liquid crystal layer, thereby the liquid crystal layer becomes opaque white resulting in display.
In such a liquid crystal display panel which controls degree of scattering by a difference in refractive index between the liquid crystal and the polymer material to indicating a display, it is difficult to obtain an excellent contrast ratio between a scattering state and a transmission state in either case where an external light is utilized or where an auxiliary light source is utilized.
Moreover, it is more difficult to obtain an excellent contrast by a simple structure, such a liquid crystal display panel has not used in a timepiece having an auxiliary light source at present. Therefore, it is desired to achieve an excellent contrast ratio by a simple structure in either case where an external light is utilized or where an auxiliary light source is utilized.
In light of the present situation as described, the present invention is made, and an object thereof is to provide a liquid crystal display panel for a timepiece capable of displaying time information and calendar information, also capable of a color display, and excellent in apparent design with a simple structure, high brightness, and excellent contrast, regardless of the presence or absence of an auxiliary light source, by utilizing a light scattering type liquid crystal cell.
To achieve the above object, in the present invention, a light scattering type liquid crystal cell is structured by respectively forming an opposed electrode on a first substrate of a pair of transparent substrates and a signal electrode on a second substrate, and sealing a liquid crystal layer containing a liquid crystal and a polymer material between the first substrate and the second substrate to form pixel portions at intersections between the signal electrode and the opposed electrode.
A liquid crystal display panel for a timepiece is structured by placing a reflector on the side of a face, on which the opposed electrode is not formed, of the first substrate constituting the light scattering type liquid crystal cell.
An excellent contrast ratio can be obtained also with the light scattering type liquid crystal cell by strong reflected light by the reflector.
Provision of a color film with a low scatterability between the first substrate and the reflector enables a color display.
Moreover, a light-accumulating source having elements for absorbing light energy and emitting light in different wavelengths can be also provided between the first substrate and the reflector, on the side opposite to the first substrate with respect to the reflector, or in the liquid crystal layer.
A reflector for transmitting a portion of light is employed as the above reflector, thereby facilitating a color display and indicating a transmission-type display.
In the above case, a light absorption film is preferably provided on the side opposite to the first substrate with respect to the reflector.
A color filter is preferably placed on the first substrate side or on the opposite side thereof with respect to the reflector for transmitting a portion of light.
A light-accumulating source having elements for absorbing light energy and emitting light in different wavelengths is preferably provided on the side opposite to the first substrate with respect to the reflector for transmitting a portion of light.
Provision of an auxiliary light source on the side opposite to the first substrate with respect to the reflector for transmitting a portion of light enables transmission-type display at a place with little or no ambient light.
A color film with a low scatterability is preferably provided between the reflector for transmitting a portion of light and the first substrate or the auxiliary light source.
A color filter may be provided between the reflector for transmitting a portion of light and the first substrate or the auxiliary light source.
A reflection-type polarizing film which transmits the light linearly polarized in the direction parallel to the transmission axis thereof and reflects the light linearly polarized in the direction orthogonal to the transmission axis thereof is preferably used as the reflector for transmitting a portion of light.
In the above case, it is desirable that a polarizing film is provided on the first substrate side or on the opposite side thereof with respect to the reflection-type polarizing film in such a manner that the transmission axis of the polarizing film and the transmission axis of the reflection-type polarizing film are nearly parallel or orthogonal to each other.
An auxiliary light source is preferably provided at the outermost position on the side opposite to the visible side of the light scattering type liquid crystal cell.
The reflection-type polarizing film is preferably a reflection-type polarizing film having a reflectance different in response to wavelength within the visible light region.
The reflector for transmitting a portion of light may be a reflector which selectively reflects the light having a certain wavelength in the visible light and transmits the light having the other wavelengths.
The auxiliary light source is preferably a light source having a light emission characteristic of the complementary color to the wavelengths of the color reflected by the reflector.
The reflector may be a transflective reflector.
A plurality of the transflective reflectors may be provided on the side of the face, on which the opposed electrode is not formed, of the first substrate.
The reflector in each example described above can be also made so as to demonstrate a reflection characteristic different between at a region where the scattering characteristic and the transmission characteristic are controlled and at a region where the scattering characteristic or the transmission characteristic is always demonstrated, by applying a voltage to the liquid crystal layer of the light dispersed type liquid crystal cell through the opposed electrode and the signal electrode.